Optical coherence tomography OCT serves to provide a one-, two- or three-dimensional (1D, 2D or 3D) tomogram of an object to be investigated. A coherent light beam with a defined coherence length is directed along an object arm onto the object. The object reflects or scatters the light of the light beam into different measuring depths. A reflection or scatter occurs especially on optical boundary surfaces of the object, on which the refraction index of the object changes. The light scattered back from the object is then superposed by a coherent light beam from a reference arm for obtaining an interference signal. The positions of the depth of the boundary surfaces are coded in the phase information and/or in the modulation frequency of the interference signal.
Due to a wavelength-dependent refraction index inside the object, dispersion can occur that can result in a loss of the axial resolution with increasing measuring depth. Resolution loss inside of the tomograms can blur the representation of boundary surfaces and structures of the object, whereby the latter may appear, for example, widened or smeared in the tomogram. Consequently, for example, closely adjacent boundary surfaces cannot be separated from each other with sufficient accuracy.
In order to obtain tomograms with a high resolution, the dispersion should be compensated for by, for example, purely optical measures. This can also be applicable in an adapted manner to large dispersions in high-resolution systems for certain sections or boundary surfaces.
In order to obtain dispersion-compensated raw data, equivalent optical path lengths are generated along the object arm and the reference arm, for example, by introducing identical media in the object arm and the reference arm. The dispersion can be compensated for only for a single, previously defined depth, therefore, for the passage through a fixed optical wavelength. On the other hand, dispersion compensation adapted for several depths can be generated by several optical compensations adapted to the particular depths. This requires a plurality of separate and expensive measurements with a changed optical compensation each time of the optical wavelength and/or of the dispersion for the particular depth. In addition, as a result of the plurality of separate measurements, the inherent accuracy of the position of boundary surfaces that would result from only one OCT measurement is lost.
Further information about dispersion compensation in OCT systems can be obtained from the publications listed in Appendix A attached hereto.